I. Field of the Invention
The invention is directed to copper foil electrodeposition cells containing organic substituent in the electrolyte. The cells may have an electrode having a first active coating layer and an additional layer that is of no significant activity. The metal can be deposited in cell operation that does not exhibit an adverse effect on electrode potential.
II. Description of the Related Art
It is well known to use coatings for electrodes having a significant quantity of platinum group metal or oxides in them that provide the electrochemical activity of a coating. However, these components are often subject to attack by substances in the electrolyte, especially substituents used in metal electrodeposition electroplating systems. Prior art devices can lose, through interaction with organic substituents in electrolytes, the coating components, as well as loss due to slow attrition of the platinum group metal from standard coatings. The slow attrition loss can be due at least in part to chemical/electrochemical dissolution.
It has, however, been found difficult to provide electrodes of extended service life, especially in electrolyte environments such as used in copper foil electrodeposition and which contain organic substituents detrimental to the stability of the components of an active coating as would contain a platinum group metal or oxide. It would, therefore, be desirable to provide an electrode capable of exhibiting extended lifetimes in such an environment. It would also be desirable to provide an electrode allowing extended electrode lifetimes while having decreased loading of the platinum group metal coating.
The present invention relates generally to an improved method for copper foil electrodeposition. The method is operational in electrolyte environments containing organic substituent, and overcomes the difficulties associated with electrode operation in such an environment, while providing more advantageous overall results.
The method uses an electrode having a topcoat layer of a valve metal oxide, which can be more stable in the electrolyte, and can minimize significant exposure of any platinum group metal or oxide in a base coating to the electrolyte, thus extending the lifetime of the electrode. This can be achieved without an adverse effect on the cell electrode potential, which was unexpected.
In one aspect, the invention is directed to a method for electrodepositing copper metal foil from an electrolyte solution having organic substituent that is contained in an electrolytic cell comprising at least one oxygen evolving anode, which method provides extended anode activity while maintaining cell electrode potential during said copper electrodeposition, which method comprises:
providing an unseparated electrolytic cell;
establishing in the cell an electrolyte containing organic substituent, and containing the copper metal in solution;
providing an anode in the cell in contact with the electrolyte which anode has multiple coating layers on an electrode base of a valve metal, the electrode base having at least one coating layer of an electrochemically active coating and at least one topcoating layer of a valve metal oxide coating or a tin oxide coating layer, whereby the active coating layer contains a first composition and the topcoating layer contains a second composition;
impressing an electric current on the anode; and
conducting the electrodeposition of the copper foil.
Still other benefits and advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed specification.
The electrolytic process of the present invention is particularly useful in the electrodeposition of copper foil, and particularly such deposition from a sulfate electrolyte. The electrode described herein when used in such an electrodeposition process will virtually always find service as an anode. Thus, the word xe2x80x9canodexe2x80x9d is often used herein when referring to the electrode, but this is simply for convenience and should not be construed as limiting the invention.
A cell using the present invention can be an electrolytic cell where a gap is maintained between electrodes, and the cell electrolyte is contained within the gap. The electrolyte as a sulfate-containing electrolyte might contain sulfuric acid or copper sulfate. The electrolyte will typically be an aqueous electrolyte, i.e., a water-based electrolyte. The copper might be dissolved in the medium of the electrolyte, such as copper sulfate dissolved in an aqueous medium.
The electrolyte will contain organic substituents. A representative constituent used in the electrodeposition of copper foil is gelatin. Such substituent might also include one or more of thiourea, amines, and animal glue. Some organic additives, as might be present, are disclosed in U.S. Pat. No. 4,469,564 to Okinaka, et al, which patent is incorporated herein by reference. As will be understood, the electrolyte ingredient for plating is copper. The one or more organic substituents are additives to the electrolyte which are generally added to the bath to improve aspects of the plating process such as deposition uniformity.
In addition to providing an unseparated cell and establishing an electrolyte containing organic substituent, plus copper metal in solution, there will be provided in the copper deposition process an anode having multiple coating layers on an electrode base of a valve metal. The layers can be represented by an active layer and at least one topcoating layer that can be a valve metal oxide coating. The active coating layer, or underlayer, contains a first composition and the topcoating layer contains a second composition. These layers will be more particularly described hereinbelow. A coating of the valve metal oxide alone generally only sustain low current densitites in cell operation. It was unexpected that in the copper foil deposition process as described herein, that such operation can sustain an elevated current density for an extended time. As representative of such operation is copper foil deposition at a current density of at least 5 kiloamps per square meter (kA/m2), and often at a density of at least 10 kA/m2, for a cell operating time of over 1,000 hours.
For the electrode having multiple coating layers, the base of a valve metal can be such metal including titanium, tantalum, zirconium, niobium, and tungsten. Of particular interest for its ruggedness, corrosion resistance and availability is titanium. As well as the normally available elemental metals themselves, the suitable metals of the electrode base can include metal alloys and intermetallic mixtures, as well as ceramics and cermets such as contain one or more valve metals. For example, titanium may be alloyed with nickel, cobalt, iron, manganese or copper. More specifically, grade 5 titanium may include up to 6.75 weight percent aluminum and 4.5 weight percent vanadium, grade 6 up to 6 percent aluminum and 3 percent tin, grade 7 up to 0.25 weight percent palladium, grade 10, from 10 to 13 weight percent plus 4.5 to 7.5 weight percent zirconium and so on.
By use of elemental metals, it is most particularly meant the metals in their normally available condition, i.e., having minor amounts of impurities. Thus, for the metal of particular interest, i.e., titanium, various grades of the metal are available including those in which other constituents may be alloys or alloys plus impurities. Grades of titanium have been more specifically set forth in the standard specifications for titanium detailed in ASTM B 265-79.
The electrode base may take various forms, i.e., any of those forms that may be used for the deposition of copper foil, and including mesh, sheet, blades, tubes or wire form. It is contemplated, that for the electrodeposition process the anode base member may be a multi-layer member, e.g., a multi-layer mesh member, such as is disclosed in U.S. Pat. No. 5,783,050, or a multi-layer member having a lead base together with a sheet member. The lead base may comprise lead or alloys of lead, such as lead alloyed with tin, silver, antimony, calcium, strontium, iridium, lithium or tellurium.
Regardless of the metal selected and the form of the anode base member, the surface of such substrate member advantageously is a cleaned surface. This may be obtained by any of the known treatments used to achieve a clean metal surface.
When a cleaned surface, or prepared and cleaned surface has been obtained, and particularly for applying the necessary multiple coating layers which will be on the valve metal base, the base surface may be further treated for enhanced adhesion such as of the electrocatalytic coating layer to the valve metal. This will be achieved by means which include intergranular etching of the substrate metal, sharp grit blasting of the metal surface, or plasma spraying, followed by surface treatment to remove embedded grit.
To prepare a metal such as titanium for etching, it can be most useful to condition the metal, as by annealing, to diffuse impurities to the grain boundaries. Thus, by way of example, proper annealing of grade 1 titanium will enhance the concentration of the iron impurity at grain boundaries. Also for the aspect of etching, it can be desirable to combine a metal surface having a correct grain boundary metallurgy with an advantageous grain size. Again, referring to titanium as exemplary, at least a substantial amount of the grains having grain size number within the range of from about 3 to about 7 is advantageous. Grain size number as referred to herein is in accordance with the designation provided in ASTM E 112-84. A serviceable metal substrate of this condition has been disclosed in U.S. Pat. No. 5,167,788.
Etching will be with a sufficiently active etch solution. Typical etch solutions are acid solutions. These can be provided by hydrochloric, sulfuric, perchloric, nitric, oxalic, tartaric, and phosphoric acids as well as mixtures thereof, e.g., aqua regia. Other etchants that may be utilized include caustic etchants such as a solution of potassium hydroxide/hydrogen peroxide, or a melt of potassium hydroxide with potassium nitrate. Following etching, the etched metal surface can then be subjected to rinsing and drying steps.
It has also been found that a suitably roughened metal surface can be obtained by special grit blasting with sharp grit followed by removal of surface embedded grit. The grit, which will contain usually angular particles, will cut the metal surface as opposed to peening the surface. Serviceable grit for such purpose can include sand, aluminum oxide, steel and silicon carbide. Upon grit removal, this can provide a suitably roughened, three-dimensional surface. Etching, or other treatment such as water blasting, following grit blasting can remove embedded grit and provide the desirably roughened surface.
In plasma spraying for a suitably roughened metal surface, although the material will be applied in particulate form such as droplets of molten metal, the feed material, e.g., a metal to be applied, may be in different form such as wire form. This is to be understood even though for convenience, application will typically be discussed as material applied in particulate form. In this plasma spraying, such as it would apply to spraying of a metal, the metal is melted and sprayed in a plasma stream generated by heating with an electric arc to high temperatures in inert gas, such as argon or nitrogen, optionally containing a minor amount of hydrogen. It is to be understood by the use herein of the term xe2x80x9cplasma sprayingxe2x80x9d that although plasma spraying is preferred the term is meant to include generally thermal spraying such as magnetohydrodynamic spraying, flame spraying and arc spraying, so that the spraying may simply be referred to as xe2x80x9cmelt sprayingxe2x80x9d. A substrate of a plasma sprayed surface morphology that can find use herein has been disclosed in U.S. Pat. No. 5,324,407.
It will be understood that the anode base surface may then proceed through various operations, including pretreatment before coating. For example, the surface may be subjected to a hydriding or nitriding treatment. Prior to coating with an electrochemically active coating, it has been proposed to provide an oxide layer by heating the substrate in air or by anodic oxidation of the substrate as described in U.S. Pat. No. 3,234,110. European patent application No. 0,090,425 proposes to platinum electroplate the substrate to which then an oxide of ruthenium, palladium or iridium is chemideposited. Various proposals have also been made in which an outer layer of electrochemically active material is deposited on a sublayer which primarily serves as a protective and conductive intermediate. U.K. Patent 1,344,540 discloses utilizing an electrodeposited layer of cobalt or lead oxide under a ruthenium-titanium oxide or similar active outer layer. Various tin oxide based underlayers are disclosed in U.S. Pat. Nos. 4,272,354, 3,882,002 and 3,950,240. It is also contemplated that the anode base surface may be prepared as with an antipassivation layer.
Following any of the hereinabove discussed considerations for the anode base surface preparation, the electrochemically active coating may then be applied to the anode base member. As representative of the applied electrochemically active coating, or xe2x80x9cfirst compositionxe2x80x9d as such term is used herein, are those provided from platinum or other platinum group metals or they can be represented by active oxide coatings such as platinum group metal oxides, magnetite, ferrite, cobalt spinel or mixed metal oxide coatings. Such coatings have typically been developed for use as anode coatings in the industrial electrochemical industry. They may be water based or solvent based, e.g., using alcohol solvent. Suitable coatings of this type have been generally described in one or more of the U.S. Pat. Nos. 3,265,526, 3,632,498, 3,711,385, and 4,528,084. The mixed metal oxide coatings can often include at least one oxide of a valve metal with an oxide of a platinum group metal including platinum, palladium, rhodium, iridium and ruthenium or mixtures of themselves and with other metals. Further coatings include manganese dioxide, lead dioxide, cobalt oxide, ferric oxide, platinate coatings such as MxPt3O4 where M is an alkali metal and x is typically targeted at approximately 0.5, nickel-nickel oxide and nickel plus lanthanide oxides.
The electrocatalytic coating may serviceably be an iridium oxide, or the coating will contain an iridium oxide together with tantalum oxide. Also serviceable are those coatings containing an element of ruthenium oxide in combination with titanium oxide itself or with iridium oxide. These coating compositions are well known in the art and have been disclosed such as in U.S. Pat. Nos. 3,632,498, 3,751,296, 3,778,307, 3,840,443 and 3,933,616, and U.S. Pat. Nos. 3,878,083 and 3,926,751.
Regardless of the coating composition chosen, the preferred coating composition solutions are typically those comprised of TaCl5, IrCl3 and hydrochloric acid, all in aqueous solution. Alcohol based solutions may also be employed. Thus, the tantalum chloride can be dissolved in ethanol or isopropanol and this mixed with the iridium chloride dissolved in either isopropanol or butanol, all combined with small additions of hydrochloric acid.
It is contemplated that any of the multiple coating layers utilized herein will be applied by any of those means which are useful for applying a liquid coating composition to a metal substrate. Such methods include dip spin and dip drain techniques, brush application, roller coating and spray application such as electrostatic spray. Moreover, spray application and combination techniques, e.g., dip drain with spray application can be utilized. With the above-mentioned coating compositions for providing an electrochemically active coating, a roller coating operation can be most serviceable.
Regardless of the method of application of the coating, conventionally, the foregoing coating procedure is repeated to provide a uniform, more elevated coating weight than achieved by just one coating. By uniform, it is meant that the undercoating layer will comprise a layer containing a single composition, e.g., a coating derived from TaCl3 and IrCl3 without other metal or metal oxide constituency. Usually, the number of coats for a representative electrochemically active coating layer of a type as mentioned hereinbefore, such as formed by thermal decomposition, will not exceed about 50 coats, and be preferably, for the amount of electrochemically active coating will not exceed 50 grams per square meter (g/m2), basis the metal content of the coating, e.g., the platinum group metal content of the coating..
Following any of the foregoing coating procedures, upon separation from the liquid coating composition, the coated metal surface may simply dip drain or be subjected to other post coating technique such as forced air drying. Additionally, the first coating layer may be cured following coating. Typical curing conditions for electrocatalytic coatings can include cure temperatures of from about 300xc2x0 C. up to about 600xc2x0 C. Curing times may vary from only a few minutes for each coating layer up to an hour or more, e.g., a longer cure time after several coating layers have been applied. However, cure procedures duplicating annealing conditions of elevated temperature plus prolonged exposure to such elevated temperature, are generally avoided for economy of operation. In general, the curing technique employed can be any of those that may be used for curing a coating on a metal substrate. Thus, oven curing, including conveyor ovens may be utilized. Moreover, infrared cure techniques can be useful. Preferably for most economical curing, oven curing is used and the cure temperature used for electrocatalytic coatings will be within the range of from about 450xc2x0 C. to about 550xc2x0 C. At such temperatures, curing times of only a few minutes, e.g., from about 2 to 10 minutes, will most always be used for each applied coating layer, although longer times of up to about 60 minutes may be utilized.
Subsequent to the formation of the first coating layer of an electrochemically active coating, there can then be formed the topcoating layer of a xe2x80x9csecond compositionxe2x80x9d as such term is used herein. As will be understood by the use of these terms, the second composition layer will differ from the first composition layer. Such second composition layer can be a valve metal oxide, or tin oxide, or mixtures thereof, which tin oxide will be more particularly discussed further on hereinbelow. The topcoating layer will typically be formed from a valve metal alchoxide in an alcohol solvent, with or without the presence of an acid. Such valve metal alchoxides which are contemplated for use in the present invention include methoxides, ethoxides, isopropoxides and butoxides. For example, titanium butyl orthotitanate, titanium ethoxide, titanium propoxide, tantalum ethoxide, or tantalum isopropoxide may be useful. Additionally, salts of the dissolved metals may be utilized, and suitable inorganic substituents can include chlorides, iodides, bromides, sulfates, borates, carbonates, acetates, and citrates, e.g., TiCl3, TiCl4 or TaCl5, in acid solution.
Where titanium oxide will be utilized, it will generally be a readily commercially available oxide such as rutile titanium dioxide. However, it is contemplated that titanium suboxide can be useful, i.e., TiOx where x is a number between 1.5 and 1.999. It is also contemplated that valve metal oxide may be used with doping agents, such as those which would be incorporated as doping agent precursors into the composition to increase the conductivity of the resulting valve metal oxide layer. For example a niobium salt may be used to provide a niobium doping agent in ion form in the oxide lattice. Other doping agents include ruthenium, iridium, platinum, rhodium and palladium, as well as mixtures of any of the doping agents. Such doping agent for the valve metal oxide may typically be present in an amount from about 0.1% to about 10%, by weight.
As mentioned hereinbefore, it is also contemplated that the topcoating layer may be a tin oxide layer. Where tin oxide is the desired topcoating layer, suitable precursor substituents can include SnCl4, SnSO4, or other inorganic tin salts. The tin oxide may be used with doping agents, such as those which would be incorporated as doping agent precursors into the composition to improve conductivity. For example a niobium salt may be used to provide a niobium doping agent in ion form in the oxide lattice. Other doping agents include ruthenium, iridium, platinum, rhodium and palladium, as well as mixtures of any of the doping agents. Doping agents suitable for a tin oxide barrier layer include antimony, indium, fluorine, chlorine, molybdenum, tungsten or tantalum. Where a doping agent is utilized, in a tin oxide topcoating layer, the doping agent will typically be present in an amount by weight of from about one percent to about twenty percent doping element as an oxide. A preferred range of doping agent is from about 0.1% percent to about 10% percent, by weight.
Following application of the topcoating layer such as of valve metal oxide, which layer may be applied in any manner as hereinbefore described with respect to the first electrochemically active coating layer, the topcoating layer may then proceed through thermal treatment. Where salts of the valve metals are utilized, this thermal treatment may be as by thermal oxidation of the valve metal salts applied to the first electrochemically active coating layer. Thermal treatment will generally be conducted in an oxygen containing environment, preferably air for economy, by heating at a temperature within the range of from greater than about 250xc2x0 C. up to about 1000xc2x0 C. For efficient thermal conversion, a preferred heating temperature will be in the range of from about 350xc2x0 C. to about 700xc2x0 C. Where the coating is applied as a liquid medium, such thermal treatment will serviceably be observed after each applied coating with such temperature being maintained from about 1 minute to about 60 minutes per coat. However, it is within the concept of the present invention that thermal treatment could occur after a successive number of coating cycles have occurred. Preferably, for efficiency and economy, the temperature will be maintained from about 3 to about 10 minutes per coat. The number of coating cycles can vary but most typically the required amount of valve metal oxide layer, with 1 to 20 coats being usual, although fewer coatings, and even a single coating, is contemplated.
Usually, the number of coats for a representative valve metal oxide coating, such as formed by the thermal decomposition of titanium butyl orthotitanate, will not exceed on the order of about 20, and advantageously for economy will not exceed about 10. However, a plurality of layers may be applied to the electrochemically active coating layer so as to provide the desired loading of valve metal oxide coating.
In a procedure also requiring heat application, and thus not completely unlike thermal oxidation of an applied precursor, it is also contemplated to form a suitable valve metal oxide layer by a chemical vapor deposition method. For this method, there can be utilized a suitable volatile starting material such as one of the organic titanium compounds mentioned hereinabove with the thermal oxidation procedure, e.g., titanium butyl orthotitanate, titanium ethoxide or titanium propoxide. In this chemical vapor deposition method for obtaining a valve metal oxide layer, the volatile starting material can be transported to a suitably prepared roughened and coated surface by an inert carrier gas, including nitrogen, helium, argon, and the like. This compound is transported to a heated substrate which is heated to a temperature sufficient to oxidize the compound to the corresponding oxide. For application of organic titanium compound, such temperature can be within the range from about 250xc2x0 C. to about 650xc2x0 C. As has been discussed hereinbefore with thermal oxidation treatment, it is also suitable to utilize in the chemical vapor deposition procedure a doping compound. Such doping compounds have been discussed hereinabove. For example, a volatile niobium compound may be added to the carrier gas transporting the volatile starting material, or such may be applied to the heated substrate by means of a separate carrier gas stream. As with the thermal oxidation process, this chemical vapor deposition procedure is most particularly contemplated for use following preparation of a suitably prepared roughened and coated surface, with the roughness being obtained such as by etching, or by sharp grit blasting, or by melt spraying of metal.
As discussed hereinbefore, the present invention is directed to the operation of electrolytic cells containing organic substituents as additives in the electrolyte within the cell. It is directed to electrolytic cells utilized in copper foil production. It is, however, contemplated that the invention may find general utility in methods of electrowinning, i.e., in operating a cell for the recovery of a metal from a cell electrolyte that contains organic substituent. Metals for recovery include the aforementioned copper, as well as cobalt, zinc, nickel, manganese, silver, lead, gold, platinum, palladium, tin, aluminum, chromium, and iron. Moreover, it is contemplated that the method of the present invention may find use in a metal electrodeposition processes such as plating, e.g., the electroplating of metals such as zinc, cadmium, chromium, nickel, and tin, as well as metal alloys such as nickel-zinc, onto a substrate, wherein the cell has an organic substituent-containing electrolyte. The substrate may be a moving substrate and the electrodeposition in such process can include electrogalvanizing or electrotinning. In such method, it is contemplated that the active coating layer may be topcoated as described hereinabove, but such topcoating can include coating with lanthanide oxides and oxides of spinels or garnets may be used.
It is also contemplated that the electrode utilized in the invention process may have a multi-layered electrode base having the valve metals of the electrode on a base of lead or alloys of lead, such as lead alloyed with tin, silver, antimony, calcium, strontium, indium or lithium. The lead base is usually in a flat sheet form and the sheet is virtually always a solid sheet. However, other forms are contemplated. Thus, for example, the lead base may have a cylindrical form or the like, such as elliptical. Still other forms of the lead base may include a perforate base and form a flow-through electrode. As a sheet form base, the sheet will usually have a thickness within the range of from about xe2x85x9 inch to about 2 inches, but some lead base electrodes can have thickness of up to about 2 feet or more. In general, such electrodes have been disclosed in U.S. patent application Ser. No. 09/273,981, now No. 6,139,705, the disclosure of which is incorporated herein by reference.
The following examples, unless otherwise noted as comparative examples, generally demonstrate the protection of the iridium components of an electrochemically active coating during operation in an electrochemical cell containing an electrolyte comprising H2SO4 with a gelatin additive: